The present invention relates to a heat insulation sleeve for use in a copying machine, an electrophotographic apparatus such as a laser beam printer or the like, and a bearing device for use in a fixing roller using the heat insulation sleeve.
In the electrophotographic apparatus, toner is attached to an electrostatic latent image formed by an optical means, and then a toner image is transferred and fixed to a copy sheet. In the fixing stage, the toner image is passed between a fixing roller incorporating a heater and a press roller.
Thereby, a transferred toner image is fused and fixed to the copy sheet.
FIG. 7 shows an example of a heating-fixing device of the electrophotographic apparatus.
A fixing roller 4 is made of a soft metal and incorporates a linear or bar-shaped heater 6 at the center of its shaft. The fixing roller 4 has a cylindrical projected small-diameter shaft portion 4a at each end thereof. The fixing roller 4 is formed of a metal material such as aluminum or an aluminum alloy (A5056, A6063) superior in thermal conductivity. Turning or polishing finishes the surface of the cylindrical surface of the fixing roller 4. The surface of the metal material is coated with resin such as fluorine plastics having a high degree of unadhesiveness. The fixing roller 4 is rotatably supported by a housing 7 at the small-diameter shaft portion 4a through a rolling bearing 5 such as a deep-groove ball bearing. The heating-fixing device has a gear 8, receiving a rotational force, provided at an end side thereof outward from the rolling bearing 5.
The heating-fixing device has a press roller 9 in contact and parallel with the fixing roller 4. The press roller 9 is rotatably supported at each end thereof by the housing 7 through a bearing 10. The press roller 9 is composed of a core metal such as iron, aluminum or the like coated with silicon rubber or composed of a core metal and a linear or bar-shaped heater 6 incorporated at the center of its shaft. A rolling bearing at each end thereof supports the press roller 9.
While the copy sheet is being fed between the rotating fixing roller 4 and the press roller 9 that follows the rotation of the fixing roller 4, a toner image is fixed to the copy sheet by fusing the toner to the copy sheet with the fixing roller 4.
A heat insulation sleeve 1 made of a material such as synthetic resin or ceramics having a low thermal conductivity is installed for heat release between the rolling bearing 5 and the small-diameter shaft portion 4a of the fixing roller 4.
With reference to FIG. 8 showing a conventional heat insulation sleeve, the heat insulation sleeve 1 is described below. The heat insulation sleeve 1 has a slit 2 formed thereon to circumferentially divide the heat insulation sleeve 1 into two parts. This is to prevent the fixing roller 4 from shaking by its heat expansion and contraction. The reason the heat insulation sleeve 1 is interposed between the rolling bearing 5 of the fixing roller 4 and the small-diameter shaft portion 4a thereof is to prevent the temperature distribution along the axial direction of the fixing roller 4 from becoming non-uniform and prevent the bearing from deterioration due to a high temperature. The high temperature is released from the rolling bearing 5 disposed at each end of the fixing roller 4, when the fixing roller 4 is heated.
As shown in FIG. 9, the conventional heat insulation sleeve 1 is press-fitted on the small-diameter shaft portion 4a of the fixing roller 4. This is to prevent the creep generated in the rolling bearing 5 and the small-diameter shaft portion 4a from causing the creep of the heat insulation sleeve 1 and the small-diameter shaft portion 4a. When the creep occurs in the heat insulation sleeve 1 and the small-diameter shaft portion 4a, the small-diameter shaft portion 4a is worn by the heat insulation sleeve 1, with the result that the rotation accuracy of the fixing roller 4 deteriorates.
Because the heat insulation sleeve 1 is press-fitted on the small-diameter shaft portion 4a of the fixing roller 4, the creep of the bearing 5 is caused by the rolling bearing 5 and the heat insulation sleeve 1. An inner ring of the rolling bearing 5 is treated by hardening. Thus, even though the creep of the bearing is generated due to the creep of the rolling bearing 5 and the heat insulation sleeve 1, either of the rolling bearing 5 and the heat insulation sleeve 1 is not worn.
An electrophotographic apparatus such as a copying apparatus, a laser beam printer, and the like incorporating a fixing device are demanded to have functions of performing operations at a high speed, to be lightweight, to be compact, and have a good design. In addition, they are demanded to have a function of making low noises. In particular, the purpose of the use thereof is diversified and they are used increasingly at various places such as at home. Therefore, they are demanded to make low noises more and more.
The present inventors have made researches to develop an electrophotographic apparatus generating low noises. As a result, they have found that the fixing device thereof makes noises, which has not been considered much. Attention has been paid to develop parts, constituting the electrophotographic apparatus, which make no noises or low noises. It has been found that noises are made periodically or suddenly from the periphery of the fixing device. Therefore, it is important to reduce the generation of noise in the periphery of the fixing device to develop the electrophotographic apparatus that makes a low noise.
In recent years, the development of a color copying apparatus is progressing rapidly. Thus, the development of the electrophotographic apparatus is greatly demanded to have uniform and high temperature distribution. In this situation, a rolling bearing having a heat insulation sleeve installed thereon is used for a press roller.
However, in recent years, the power source of the electrophotographic apparatus or the like is turned off frequently at short intervals for energy saving. Thus, the power source for heating the fixing roller is turned on and off frequently at short intervals. In a rolling bearing device for use in such a fixing roller, the heat insulation sleeve is broken at the root of a flange thereof, which dislocates the fixing roller axially and thus deteriorates image quality.
The present invention has been made in view of the above-described situation. Thus, it is an object of the present invention to provide a heat insulation sleeve and a bearing device for a fixing roller capable of reducing the degree of generation of periodical or sudden noises that are generated in the periphery of a fixing device.
It is another object of the present invention to provide a heat insulation sleeve and a bearing device for a fixing roller preventing a flange of the heat insulation sleeve from being broken when the heat insulation sleeve and bearing device for a fixing roller are incorporated in an electrophotographic apparatus which is heated and cooled frequently at short intervals.
The heat insulation sleeve of the present invention is interposed between a fixing roller and a rolling bearing rotatably supporting the fixing roller at each end thereof The heat insulation sleeve has a slit dividing the heat insulation sleeve at one position in a circumferential direction of the heat insulation sleeve, and each end of the slit overlap each other in an axial direction of the heat insulation sleeve.
Further, the heat insulation sleeve has a flange and a projection. The flange is formed at one end of a cylindrical portion thereof and the projection at a peripheral end of the cylindrical portion.
The bearing device of the present invention for a fixing roller rotatably supporting the fixing roller comprises a heat insulation sleeve and a rolling beating. The heat insulation sleeve is interposed between a small-diameter portion of the fixing roller disposed at each end thereof and an inner ring of a rolling bearing, and is press-fitted on the inner ring of the rolling bearing.
Further, the heat insulation sleeve has a means for preventing the heat insulation sleeve from moving axially relative to the rolling bearing on a fit-on surface of the heat insulation sleeve that is fitted on a fit-on surface of the rolling bearing.